/* deadlock1.c SJ

   An example of poor communication practice 
*/
   
#include <stdio.h>
#include <mpi.h>

/* a variable needeed for call, result not used */
static MPI_Status tmpstat;

int main(int argc, char **argv)
{
  int PID,	/* process-ID */
	  P;	/* number of processes */ 

  /* own variables */

  int v1 = 1, v2, other;

  /* keep these 3 calls */
  MPI_Init(&argc, &argv);
  MPI_Comm_rank(MPI_COMM_WORLD, &PID);
  MPI_Comm_size(MPI_COMM_WORLD, &P);

  /* actual code */

  if (P == 2) {

	  other = 1-PID;

	  /* this DEADLOCKS if MPI_Send() is blocking */
	  MPI_Send(&v1, 1, MPI_INT, other, 0, MPI_COMM_WORLD);
	  MPI_Recv(&v2, 1, MPI_INT, other, 0, MPI_COMM_WORLD, &tmpstat);

	  printf("%d: sent:%d received:%d\n", PID, v1, v2);

	  /* this DEADLOCKS as MPI_Ssend() is blocking */
	  /* MPI_Ssend(&v1, 1, MPI_INT, other, 0, MPI_COMM_WORLD); */
	  /* MPI_Recv(&v2, 1, MPI_INT, other, 0, MPI_COMM_WORLD, &tmpstat); */
	  /* printf("%d: sent:%d received:%d\n", PID, v1, v2); */

	  /* this would DEADLOCK ALWAYS as MPI_Recv is always blocking */
	  /* MPI_Recv(&v2, 1, MPI_INT, other, 0, MPI_COMM_WORLD, &tmpstat); */
	  /* MPI_Send(&v1, 1, MPI_INT, other, 0, MPI_COMM_WORLD); */
	  /* printf("%d: sent:%d received:%d\n", PID, v1, v2); */

  } else {
	  printf("This example works only for 2 processes\n");
  }

  /* keep this call */
  MPI_Finalize();

  exit(0);

}